1. Technical Field
Photoresist monomers, polymers derived from the same and photoresist compositions comprising the polymers are discussed. In particular, photoresist monomers, polymers derived from the same and photoresist compositions comprising the polymers that are suitable for photolithography processes using DUV (deep ultraviolet light sources) are disclosed.
2. Description of the Background Art
Recently, chemical amplification type DUV photoresists have been investigated in order to achieve high sensitivity in minute image formation processes for preparing semiconductor devices. Such photoresists are prepared by blending a photoacid generator and matrix resin polymer having an acid labile group.
According to the reaction mechanism of such a photoresist, the photoacid generator generates acid when it is illuminated by a light source, and the main chain or branched chain of the resin is reacted with the generated acid to be decomposed or crosslinked. The polarity change of the resin induces solubility differences between the exposed portion and unexposed portion in the developing solution, to form a predetermined pattern.
In the lithography process, resolution depends upon the wavelength of the light source; the shorter the wavelength, the more minute pattern can be formed.
In general, a photoresist (hereinafter, abbreviated to as xe2x80x9cPRxe2x80x9d) must satisfy various requisites such as low absorbance to the light source, excellent etching resistance, heat resistance and adhesiveness, and more preferably, it should be developable in 2.38 wt % aqueous tetramethylammonium hydroxide (TMAH) solution. However, it is very difficult to synthesize a polymer that satisfies all of these requisites. For example, a polymer having a polyacrylate main chain can be easily synthesized, but it has poor etching resistance and has difficulties in the developing process. In order to secure etching resistance, adding an alicyclic unit to the main chain has been considered. However, in this case, it is very difficult to form a copolymer wherein the main chain is comprised entirely of alicyclic units.
As an attempt to solve the problems described above, Bell Research Center developed a polymer having the following chemical structure, wherein the main chain is substituted with norbornylene, acrylate and maleic anhydride units. 
However, the above polymer has a problem in that the maleic anhydride moiety (xe2x80x98Axe2x80x99 portion), which is employed to polymerize alicyclic olefin groups, is readily dissolved in 2.38 wt % aqueous TMAH solution even in an unexposed condition. Thus, in order to inhibit the dissolution of the polymer in the unexposed section, the ratio of xe2x80x98Yxe2x80x99 portion having tert-butyl substituent should be increased, but this results in a relative decrease of the xe2x80x98Zxe2x80x99 portion (which has a role of increasing adhesiveness to the substrate), and therefore the PR might be easily separated from the substrate at the time of patterning.
In order to solve the problem, cholesterol type dissolution inhibitors have been added to the polymer to form a two-component system. However, since the amount of the dissolution inhibitor is very high (about 30%(w/w) of the resin), reappearance is low and the production cost is high, thereby making the system unsuitable as a PR.
Novel PR monomers are disclosed that can form polymers having excellent etching resistance, adhesiveness and photosensitivity, and can be manufactured on a large scale at a low production cost.
PR polymers having excellent etching resistance, adhesiveness and photosensitivity, and a process for preparing the same are also disclosed.
Photoresist compositions using the PR polymers described above, and a process for preparing the same are also disclosed.
A semiconductor element produced using the photoresist composition is also disclosed.